device_watcher_init()
=====================

The ``device_watcher_init()`` function is the initialization function for the driver. It is responsible for registering the PCI driver with the kernel when the module is loaded.

Function Signature
------------------

.. code-block:: c

   static int __init device_watcher_init(void);

- **static**: The function is only visible within this file.
- **__init**: Indicates that this function is used only during initialization and can be discarded after the driver is loaded.
- **Returns**: An integer, typically ``0`` on success or a negative error code on failure.

Purpose
-------

The ``device_watcher_init()`` function registers the PCI driver with the kernel using the ``pci_register_driver()`` function. This allows the kernel to associate the driver with the PCI devices it supports.

Implementation
---------------

.. code-block:: c

   static int __init device_watcher_init(void) {
       return pci_register_driver(&pci_watcher_driver);
   }

- The function calls ``pci_register_driver()`` and passes the ``pci_watcher_driver`` structure as an argument.
- The ``pci_watcher_driver`` structure contains the driver's name, the device ID table (``pci_watcher_ids``), and the probe and remove functions.
- The return value of ``pci_register_driver()`` is returned directly. If successful, it returns ``0``; otherwise, it returns an error code.

Error Handling
--------------

- The function does not explicitly handle errors. If ``pci_register_driver()`` fails, the error is propagated to the caller (typically the kernel's module loading mechanism).

Usage
-----

- This function is called when the driver module is loaded using the ``insmod`` or ``modprobe`` command.
- It is paired with the ``device_watcher_exit()`` function, which is called when the module is unloaded.

Example Usage
-------------

When the driver is loaded, the kernel calls ``device_watcher_init()``, which registers the driver with the PCI subsystem. If successful, the driver is now ready to handle PCI devices that match the IDs in the ``pci_watcher_ids`` table.

Summary
-------

The ``device_watcher_init()`` function is a critical part of the driver's initialization process. It registers the driver with the kernel's PCI subsystem, enabling the driver to manage the supported PCI devices. The function is simple and relies on the ``pci_register_driver()`` function to perform the actual registration.